The present disclosure relates to an image reading apparatus for detecting the size of a document sheet placed on a document sheet mounting surface, an image forming apparatus, and a document sheet width detecting method.
In general, in an image reading apparatus such as a scanner that can read an image from a document sheet, the size of a document sheet placed on a document sheet mounting surface may be detected before an image reading process is executed. For example, there is known a technology for detecting the size of a document sheet by reading image data by irradiating light from a reading unit immediately before a document sheet cover is closed by the user, and identifying a document sheet area and an out-of-document-sheet area from the read image data.